This application relates generally to magnetic disc drives and more particularly to a disc drive disc clamp assembly having a base, retainer and balance ring.
Disc drives are data storage devices that store digital data in magnetic form on a storage medium on a rotating information storage disc. Modern disc drives include one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (xe2x80x9cheadsxe2x80x9d) mounted to a radial actuator for movement of the heads relative to the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The read/write transducer, e.g., a magnetoresistive read/write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment.
The heads are mounted via flexures at the ends of a plurality of actuator arms that project radially outward from the actuator body. The actuator body pivots about a shaft mounted to the disc drive housing at a position closely adjacent the outer circumference of the information storage discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the information storage discs, so that when the actuator arms are pivoted, the heads move in an arc across the surfaces of the information storage discs.
As briefly noted above, modem disc drives include one or more information storage discs mounted on the spindle motor. Spacers are typically mounted on the spindle motor between information storage discs to provide adequate separation between the information storage discs for allowing the actuator arms and the attached flexures to position two heads against adjacent disc surfaces. The information storage discs and spacers collectively form a disc stack, or disc pack, that is mounted on the spindle motor hub and held together with a disc clamp to form the spindle motor hub assembly.
It is critical in the disc drive industry, especially in light of increased spindle motor speeds, to not only have the disc stack secured to the spindle hub, but to have an overall balanced spindle hub assembly, i.e., where the center of gravity of the spindle hub assembly is positioned at or close to the central axis of rotation of the spindle hub. Imbalance within the spindle hub assembly may cause undue and uneven wear on the spindle motor and may result in rotational vibrations within the disc drive. Rotational vibrations may cause undesired variations in the read/write signals detected by the read/write heads and may result in unwanted noise emissions from the disc drive.
The overall balance of a spindle hub assembly results from imbalances contributed by the information storage discs, the disc spacers, the hub itself, the disc clamp and the clamping force applied by the disc clamp, or any combination of the above imbalances of the above. Improved disc clamp design has helped improve the overall balance of the spindle hub assembly, especially with regard to manufacturing of disc clamps that provide a more uniform vertical clamping force. Additionally, recent aluminum disc clamp designs have introduced a balancing structure that modifies the disc stack center of gravity to be positioned toward the central axis of spindle hub rotation. However, these newer disc clamp designs often require complex and costly fabrication methods.
Accordingly, there is a need in the art for a relatively inexpensive disc clamp having a balancing structure for balancing the spindle hub assembly.
Against this backdrop the present invention has been developed. In one embodiment, the invention is a disc clamp assembly for exerting a clamping force on a disc stack to secure the disc stack to a spindle hub, where the disc clamp assembly, disc stack, and spindle hub combine to form a spindle hub assembly. The disc clamp assembly modifies the center of gravity of the spindle hub assembly toward a central axis of rotation of the spindle hub, and includes a disc shaped base piece having a top surface and a bottom surface, the bottom surface for contacting a top surface of the spindle hub. The base piece also includes a peripherally located annular ring for contacting a top information storage disc of the disc stack.
The disc clamp assembly also includes a disc shaped retainer piece engaged to the top surface of the base piece, the retainer piece having a peripheral balance ring receiving portion for receiving a balance ring. The balance ring having a first end and a second end with a gap formed therebetween, where the predetermined mass of the balancing ring is varied dependent on the length of the balance ring. The balance ring is secured within the peripheral balance ring receiving portion of the retainer piece to modify the center of gravity of the spindle hub assembly toward the central axis of the spindle hub.
In another embodiment, the invention is a balance ring retainer for balancing a spindle hub assembly, and includes an annular shaped central web portion for operative attachment to the spindle hub and a peripheral balance ring accepting portion for accepting a balancing ring. The balance ring has a first end and a second end a gap therebetween. The length of the balance ring determines the mass of the balance ring so that a balance ring is selected to improve the balance of the spindle hub assembly.
Finally, an embodiment of the invention is a method of balancing a spindle hub assembly within a disc drive. The method includes the steps of assembling a disc stack on a spindle hub of a disc drive spindle motor; assembling a disc clamp assembly having a base piece and a balance ring retainer piece; positioning the disc clamp assembly on the spindle hub so that the base piece engages both the spindle hub and a top surface of an information storage disc in the disc stack; determining the center of gravity of a spindle hub assembly comprising the assembly of the spindle hub, the disc stack, and the disc clamp assembly; and positioning a balance ring having a predetermined mass in the balance ring retainer piece of the disc clamp of the disc clamp assembly to move the center of gravity of the spindle hub assembly toward the central axis of rotation for the spindle hub assembly.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.